Visual variables

Color

A color variable overrides the color of a symbol based on a numeric data value returned from a field or expression along a continuous color ramp. Numeric data should be normalized before visualizing it with color, especially for polygon layers.

Color visual variables require the following:

1. A reference to a data value either from a field name, or an Arcade expression.
2. At least two color stops that match data values to colors. The colors of symbols with data values between the designated stops are linearly interpolated.

The following example renders the current temperature reported by weather stations along a continuous color ramp.

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          visualVariables: [
            {
              type: "color",
              field: "TEMP",
              stops: [
                { value: 20, color: "#2b83ba" },
                { value: 35, color: "#abdda4" },
                { value: 50, color: "#ffffbf" },
                { value: 65, color: "#fdae61" },
                { value: 80, color: "#d7191c" }
              ]
            }
          ]

Size

A size variable overrides the size of a symbol based on a numeric data value returned from a field or expression. This does not apply to renderers with fill symbols. To visualize a polygon layer by size, you should use a marker symbol, which will be rendered at the centroid of the polygon.

The size visual variable can be defined in two different ways:

1. With size stops, or
2. Matching a maxDataValue with a maxSize, and a minDataValue with a minSize.

Size visual variables require the following:

1. A reference to a data value either from a field name, or an Arcade expression.
2. At least two size stops that match data values to sizes. The sizes of symbols with data values between the designated stops are linearly interpolated.

The following example renders the current wind speed reported by weather stations along a continuous size ramp.

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          visualVariables: [
            {
              type: "size",
              field: "WIND_SPEED",
              minDataValue: 5,
              maxDataValue: 60,
              minSize: 4,
              maxSize: 22
            }
          ]

Rotation

A rotation variable sets the rotation of a symbol based on a numeric data value returned from a field or expression. This is typically done to rotate symbols that indicate directionality, such as:

• wind direction
• traffic flow
• aspect

Rotation visual variables are different from other visual variables in that they only require a data value without the need for stops.

1. A reference to a data value either from a field name, or an Arcade expression.
2. An optional rotation type indicating a geometry or arithmetic rotation.

The following example visualizes weather stations with arrow markers and rotates them based on wind direction.

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          visualVariables: [
            {
              type: "rotation",
              field: "WIND_DIRECT",
              rotationType: "geographic"
            }
          ]

Opacity

An opacity variable overrides the opacity of a symbol based on a numeric data value returned from a field or expression. This variable is typically used to subdue features or make some more prominent than others.

Opacity visual variables require the following:

1. A reference to a data value either from a field name or an Arcade expression.
2. At least two opacity stops that match data values to opacity values between 0 and 1. The opacity of symbols with data values between the designated stops are linearly interpolated.

The following example visualizes the predominant crop for each U.S. county. The renderer has an opacity variable to emphasize counties with a lot of cropland and subdue counties that have very little cropland by comparison.

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          visualVariables: [
            {
              type: "opacity",
              field: "TotalFarmedAcres",
              normalizationField: "AREA_ACRES",
              legendOptions: {
                showLegend: false,
              },
              stops: [
                { value: 0.0, opacity: 0.2 },
                { value: 0.1, opacity: 0.5 },
                { value: 0.5, opacity: 0.8 },
                { value: 0.9, opacity: 1.0 }
              ]
            }
          ]